1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus and a method for assembling the magnetic recording and reproduction apparatus. In particular, the present invention relates to a magnetic recording and reproduction apparatus for performing information recording and/or information reproduction with a tape being wound around a rotatable head cylinder over a prescribed angle, and a method for assembling such a magnetic recording and reproduction apparatus.
2. Description of the Related Art
Recently, magnetic recording and reproduction apparatuses used for video tape recorders and the like have been progressively reduced in cost and increased in performance.
In general, a magnetic recording and reproductions apparatus includes a sub chassis unit, a main chassis unit, and an idler, and is produced by assembling the sub chassis unit, the main chassis unit, and the idler.
Hereinafter, with reference to FIGS. 18 through 23, a conventional magnetic recording and reproduction apparatus 200 will be described.
FIG. 18 is a plan view of a sub chassis unit 250 of the conventional magnetic recording and reproduction apparatus 200. FIG. 19 is a plan view of a main chassis unit 260 of the conventional magnetic recording and reproduction apparatus 200. FIG. 20 is a plan view of a conventional idler 235. FIG. 21 is a plan view of a conventional cover plate 242. FIG. 22 is a plan view of an assembly of the sub chassis unit 250, the main chassis unit 260 and the idler 235. FIG. 23 is a plan view of the conventional magnetic recording and reproduction apparatus 200 which is obtained by assembling the sub chassis unit 250, the main chassis unit 260 and the idler 235 and then attaching the cover plate 242 to the sub chassis unit 250.
As shown in FIG. 18, the sub chassis unit 250 includes a sub chassis 201, four tape pull-out members 202, 206, 209 and 210 provided on the sub chassis 201, a supply reel stand (S reel stand) 211 rotatably provided on the sub chassis 201, and a take-in reel stand (T reel stand) 212 rotatably provided on the sub chassis 201.
As shown in FIG. 19, the main chassis unit 260 includes a main chassis 221, a capstan 231 provided on the main chassis 221, a capstan shaft 231a provided on the capstan 231, a drive gear 232, a timing belt 233, and a center gear 234.
In the state where a pinch roller (not shown) presses a tape to the capstan shaft 231a, the capstan shaft 231a rotates to drive the tape. A capstan gear 231b is integrally provided with the capstan 231.
The drive gear 232 is supported at an axis thereof by a rotation shaft 232a provided on the main chassis 221. The drive gear 232 includes an upper gear 232b and a lower gear 232c. The timing belt 233 is extended around the upper gear 232b and the capstan gear 231b. 
The center gear 234 is supported at an axis thereof by a rotation shaft 234a provided on the main chassis 221. The center gear 234 includes an upper gear 234b and a lower gear 234a. The lower gear 232a of the drive gear 232 and the lower gear 234c of the center gear 234 are engaged with each other.
The idler 235 shown in FIG. 20 is to be mounted on the main chassis unit 260.
The idler 235 includes an idler arm 235a and an idler gear 235c. 
In the assembled state of the magnetic recording and reproduction apparatus 200, the idler arm 235a is held by the main chassis 221 to be pivotable about a pivoting shaft 235b. The idler gear 235c is held by the idler arm 235a to be rotatable with a rotation shaft 235d as the center of rotation. The idler gear 235c is pressed by an idler gear pressing section (not shown), thereby generating a rotation load torque in the idler gear 235c. 
As shown in FIG. 21, the cover plate 242 has a reel lock release member 242a on a top surface thereof. In the assembled state of the magnetic recording and reproduction apparatus 200, the reel lock release member 242a is inserted, into a cassette mounted on the sub chassis unit 250 and releases a reel lock mechanism provided in the cassette. An LED 242bis inserted into the cassette. Light emitted by the LED 242b passes through the tape in the cassette and then is sensed by photosensors (not shown) provided on both sides of the sub chassis 201. Thus, a leading end and a trailing end of the tape are detected.
FIG. 22 is a plan view of an assembly of the sub chassis unit 250, the main chassis unit 260 and the idler 235. In this example, the sub chassis unit 250 shown in FIG. 18 is stacked on the main chassis unit 260 shown in FIG. 19, and then the idler 235 for driving the supply reel stand 211 and the take-in reel stand 212 of the sub chassis unit 250 is mounted such that an axis of the idler 235 is supported by the main chassis unit 260.
FIG. 23 is a plan view of the conventional magnetic recording and reproduction apparatus 200 which is obtained by assembling the sub chassis unit 250, the main chassis unit 260 and the idler 235 and then attaching the cover plate 242 to the sub chassis unit 250. In other words, after the state shown in FIG. 22 is obtained, the cover plate 242 shown in FIG. 21 is attached to the sub chassis unit 250.
The cover plate 242 includes the reel lock releaser member 242a for releasing the reel lock mechanism in the cassette (not shown) and the LED 242b which is alight emitting device for detecting a leading end and a trailing end of the tape. Since the reel lock release member 242a and the LED 242b are inserted into the cassette when the magnetic recording and reproduction apparatus 200 is used, the reel lock release member 242a and the LED 242b need to be provided at a position closest to the cassette. Therefore, the reel lock release member 242a and the LED 242b need to be provided between the idler 235, for driving the supply reel stand 211 and the take-in reel stand 212, and the cassette.
The conventional magnetic recording and reproduction apparatus 200 needs to be assembled in the following manner. The main chassis unit 260 and the sub chassis unit 250 are assembled, then the idler 235 is mounted, and the cover plate 232 including the reel lock release member 242a and the LED 242b is attached to the sub chassis unit 250. Alternatively, the main chassis unit 260 and the sub chassis unit 250 are assembled, then the idler 235 is mounted, and the reel lock release member 242a and the LED 242b are attached to the sub chassis unit 250.
The LED 242b usually includes a flexible printed circuit board or the like attached by soldering for electric connections, and thus is large in size including a large number of components and requires a large number of steps to assemble. In consideration of the distribution costs required for assembling the components and comprehensive quality control, it is desirable that a magnetic recording and reproduction apparatus includes large units. For disassembly for maintenance or the like, it is desirable that a magnetic recording and reproduction apparatus is divided into large units. According to the structure of the conventional magnetic recording and reproduction apparatus 200, It is impossible to attach the reel look release member 242a and the LED 242b to the sub chassis 250 before the sub chassis 250 and the main chassis 260 are assembled. For this reason, the sub chassis 250 cannot be a large unit.